Electrochemical cells are widely used for electrochemical and biological applications. Typically, an electrochemical cell has a counter electrode at the top of the cell, a non-current-carrying reference electrode positioned in the central region of the cell and a working electrode positioned near the bottom of the cell. Controlling and measuring the electrical parameters of an electrode reaction in a cell is done by potential, current and charge control means. The two most common modes of operation are potential control or potentiostatic mode and the current control or galvanostatic mode. A review article by R. Greef, covering this subject matter is published in Journal of Physics E, Scientific Instruments, Vol. 11, 1978, pages 1-12 (printed in Great Britain).
When operating a potentiostat or a galvanostat with an electrochemical cell, there is a voltage drop, that is, an IR drop across the reference electrode and the working electrode. For example, whereas the voltage at the reference electrode may be 1.00 v, the corresponding voltage at the surface of the working electrode is 0.80 v. In this case, the IR drop is 0.20 volts. In order to make accurate measurements, it is necessary to provide IR compensation when operating the potentiostat and the galvanostat.
Electrochemical instruments that are available commercially that perform both as potentiostats and galvanostats can perform the IR compensation when operating as a potentiostat, but they do not perform the IR compensation when operated at a galvanostat. Thus, there is no IR compensation available for operation in the galvanostatic mode.
With high power potentiostat/galvanostat usage, high current is employed. The voltage drop across the reference electrode and working electrode across the uncompensated resistance can be extremely large.
Commercially available potentiostat/galvanostats of the type described in the instruction manual for the Princeton Applied Research Model 173 Potentiostat/Galvanostat have a number of switches in order to change the instrument from a potentiostatic operating mode to a galvanostatic operating mode. In a power potentiostat/galvanostat, the current flow through some of these switch contacts are large. Another approach to a potentiostat/galvanostat requiring less switches and which requires negligibly small currents flowing through the switch contacts, is shown in FIG. 1 and described in the copending patent application assigned to the assignee of the present invention entitled "An Improved Instrument for Use with an Electrochemical Cell" Ser. No. 049,525 filed June 18, 1979. However, neither of these prior art potentiostat/galvanostat systems provides IR compensation in the galvanostatic mode; and
FIGS. 2A and 2B are alternative embodiments of electric circuitry 46 of FIG. 2.